The primary objective of the proposed research is to study psychophysiological reactivity in traumatized children receiving treatment for posttraumatic stress disorder (PTSD) so as to better inform the assessment and treatment of posttraumatic stress in youth. Towards this goal, three specific aims will be addressed via procedures appended to a larger community-based effectiveness study of Trauma-Focused Cognitive Behavioral Therapy (TF-CBT). Given the plethora of research documenting enhanced physiological reactivity in adults with PTSD (Karl, 2006;Pole, 2007) and the scarcity of such research in youth, the first aim is to compare physiological peripheral and neural responses to threat-related pictures and acoustic startle probes in traumatized youth and non-traumatized youth and to examine the relation between physiological reactivity and PTSD severity. Given that treatment of PTSD in adults has demonstrated significant changes in physiological reactivity (Shalev, Orr, &Pitman, 1992), the second aim is to determine if completion of TF-CBT is associated with a reduction in physiological responses to threat-related pictures and acoustic startle probes, relative to the passage of time in non-traumatized youth. Parental support and engagement in treatment is a key feature of TF-CBT and reflects a body of work linking social support with resiliency and protection from the adverse effects of trauma (see Luthar &Cicchetti, 2000). Compared to youth participating in TF-CBT without a parent, youth with a participating parent have shown greater reductions in internalizing and externalizing problems following treatment (Cohen, Mannarino, Berliner, &Deblinger, 2000). The third aim is to examine the relation between perceived parental support and pre- to post-treatment changes in physiological reactivity to threatening stimuli. PUBLIC HEALTH RELEVANCE: The proposed research focuses on a seriously at-risk population of youth. The high prevalence of childhood trauma and its deleterious effects on emotional and cognitive development in youth implores efforts to improve the assessment and treatment of child traumatic stress. The proposed research informs such efforts by exploring potential physiologically-based markers of child traumatic stress and the potential for physiological reactivity to change following trauma-focused treatment. Further, the proposed research strives to elucidate the role of parental support and engagement, an important component of TF-CBT, in facilitating potential changes in physiological reactivity following treatment.